The present invention relates to specific pancreatic lipase inhibitors and to their applications in the treatment and prevention of cardiovascular diseases, of hyperlipemia and of obesity, and also as diagnostic reagent and as regulating agent in a method of controlled lipolysis of triglycerides.
Dietary fats represent an efficient source of energy for the body. Indeed, the quantity of energy metabolized from lipids is significantly greater than that metabolized from carbohydrates or proteins. However, given that practically all the lipids ingested are assimilated by the body, a dietary excess of lipids can cause substantial health disorders: cardiovascular disorders, hyperlipemias and obesity.
These disorders are frequently encountered in industrialized countries where the populations often have diets which are too high in saturated fats.
In order to combat these various pathological conditions, a dietary care consisting in limiting the ingestion of fatty substances is necessary but not always sufficient. Indeed, while some fatty substances are easy to detect and to remove from the diet (butter, oils and the like), this is considerably less true of others by virtue of their integration into the foods (meats, dairy products and the like).
In the cases where the introduction of a dietary regime proves insufficient, pharmacological treatments are then proposed. Most of the current treatments are intended in particular to combat hyperlipemias by using, inter alia, inhibitors of the synthesis of cholesterol.
However, current research is increasingly geared towards products which induce a more general inhibition of the lipolytic activity.
In such a perspective, one of the orientations which has been particularly studied is that of the inhibition of pancreatic lipase, which is a key enzyme in the digestion of dietary triglycerides; the digestion of the latter, major constituents of lipids (about 95%), which is started in the upper digestive tract by lipases of preduodenal origin (gastric lipase in humans), is essentially carried out in the intestine, under the action of pancreatic lipase. The latter converts the triglycerides to free fatty acids and to 2-monoglycerides, more polar products of hydrolysis, which are capable of crossing the enterocyte brush border membrane, after incorporation into mixed micelles of bile salts and phospholipids.
Pancreatic lipase therefore plays a role in the emergence of diseases linked to the presence of an excess of lipids, such as cardiovascular diseases, hyperlipemias and obesity, by allowing the assimilation of practically all the triglyercides ingested. In addition, it promotes the intestinal absorption of cholesterol, since the solubility of cholesterol is increased in the mixed micelles, which are high in fatty acids.
The action of pancreatic lipase comprises several stages: adsorption of the enzyme, in the intestine, onto the lipid interface, in the presence of bile salts and of a colipase, whose role is to anchor the lipase onto the interface (C. Chapus et al., FEBS Letters, 1975, 58, 1, 155-158), followed by the hydrolysis of the sn-1,3 ester bonds of the triacylglycerols.
Thus, the digestion of triglycerides involves lipase/colipase interactions regulated by a lipid interface.
Porcine lipase, for example, is a glycoprotein containing 449 amino acids, whose glycan chains are linked to asparagine (Asn) at position 166; it contains two domains separated by the Phe336-Ala337 bond (M. Bousset-Risso et al., FEBS Letters, 1985, 182, 2, 323-326). Each domain carries a recognition site, namely: an interfacial recognition site (N-terminal domain), site of the hydrolysis per se, and a recognition site for its protein partner (C-terminal domain), the colipase. The N-terminal domain (residues 1-335), which carries the active centre of the enzyme, is separated from the C-terminal domain (residues 336-449) by a narrow region which is very resistant to proteolysis. This organization into two domains corresponds to the two specific functions listed above: the N-terminal domain is responsible for catalysis, whereas the C-terminal domain is involved in the recognition of the colipase (A. Abousalham et al., Protein Engineering, 1992, 5, 1, 105-111).
The colipase is a small molecule (10 kDa) which is highly cross-linked because of the presence of 5 disulphide bridges. It carries three recognition sites which are essential for its function, namely: an interfacial recognition site (H. van Tilbeurgh et al., Nature, 1993, 362, 814-820), a lipase recognition site (C. Chaillan et al., FEBS Letters, 1989, 257, 2, 443-446; H. van Tilbeurgh et al., Nature, 1992, 359, 159-162) and a micellar recognition site (J. Hermoso et al., EMBO J., 1997, 16, 18, 5531-5536). These three sites are topologically distinct.
Extensive studies which have been carried out for many years have made it possible to increase understanding of the structure/function relationships in the pancreatic lipase/colipase system (C. Chaillan et al., 1989, cited above).
Additional structural studies relating to both human lipase (Winkler F. K. et al., Nature, 1990, 343, 771-774) and horse lipase (B. Kerfelec et al., Eur. J. Biochem., 1992, 206, 279-287; Y. Bourne et al., J. Mol. Biol., 1994, 238, 709-732) have made it possible to confirm the existence of the abovementioned two domains, in lipases of different origins.
The recognition between the lipase and the colipase involves, in particular, hydrophobic interactions (N. Mahxc3xa9-Gouhier et al., BBA, 1988, 962, 91-97) and electrostatic interactions.
Covalent coupling experiments between the pancreatic lipase and colipase (C. Chaillan et al., 1989, cited above), as well as the resolution of the three-dimensional structure at 3.1 xc3x85 of the lipase/colipase complex (H. van Tilbeurgh et al., 1992, cited above), have led to the identification of the recognition regions on the two molecules, in solution.
To inhibit pancreatic lipase and obtain a therapeutic activity on hyperlipemias and obesity, various approaches have been proposed:
the use of covalent inhibitors, which bind to the active centre of the enzyme; there may be mentioned, for example, tetrahydrolipstatin (THL), [U.S. Pat. No. 4,598,089; P. Hadvary et al., J. Biol. Chemistry, 1991, 266, 4, 2021-2027; D. Hermier et al., FEBS Letters, 1991, 286, 1, 186-188]; a complete inhibition of the lipolytic activity is obtained for doses of 1 mol of THL/mol of enzyme (P. Hadvary et al., 1991, cited above) or doses of 10 to 400 mg, twice per day (J. Hauptman et al., Am. J. Clin. Nutr., 1992, 55, 309S-313S); such a method has a number of disadvantages, of which the main one is the lack of specificity; tetrahydrolipstatin is indeed not specific for pancreatic lipase and inhibits other lipases such as carboxylester lipase, gastric lipase and lipase stimulated by the bile salts in human milk; and
the modification of the nature of the interface by addition of amphiphilic proteins (Gargouri Y. et al., J. Biol. Chem., 1985, 260, 2268-2273); of detergents (Gargouri Y. et al., J. Lip. Res., 1983, 24, 1336-1342) or of fibres (Borel P. et al., Am. J. Clin. Nutr., 1989, 49, 1192-1202); such a method has a very relative efficiency.
These two approaches comprise, in addition, a significant risk of undesirable effects (nausea and the like).
Consequently, the applicant set itself the objective of providing a new pancreatic lipase inhibitor which is better suited to the needs of practical application than the prior art lipase inhibitors, in particular in that it exhibits a real specificity of action towards pancreatic lipase.
The subject of the present invention is a peptide consisting of a C-terminal fragment of a pancreatic lipase, including the recognition site for a colipase (called hereinafter C-terminal peptide), for its use as medicament, in particular for the treatment of hyperlipemias, of cardiovascular diseases and of obesity.
According to an advantageous embodiment of the invention, the said peptide is a C-terminal fragment of a pancreatic lipase selected from purified or recombinant human, porcine or equine pancreatic lipases.
Unexpectedly, the C-terminal peptide of these various pancreatic lipases effectively makes it possible for them to serve as a lure and to competition between this peptide and the native lipase for the colipase and thus to significantly reduce the lipolytic action of the said lipase.
The administration of such a peptide slows down the action of the pancreatic lipase and surprisingly inhibits, at least in part, the hydrolysis of dietary triglycerides, which will therefore not be absorbed (inhibitory effect of the C-terminal peptide on the lipolysis).
Indeed, the affinity of this C-terminal peptide is, in vitro:
in solution, of the order of 106 M, towards the colipase, whereas
at the lipid interface, the affinity of the C-terminal peptide is of the order of 2xc3x97108 M.
To obtain the desired action, that is to say an affinity at the interface of the order of 2xc3x97108 M, the said C-terminal peptide is preferably administered at doses of 0.5 to 10 mg/day distributed over 1 to 3 takings, corresponding to doses of 0.2 to 10 mg per taking.
The subject of the present invention is also a pharmaceutical composition comprising the C-terminal peptide of a pancreatic lipase, including the recognition site for a colipase, as defined above and at least one pharmaceutically acceptable vehicle.
The said pharmaceutical composition is advantageously provided in a unit form capable of being administered by the oral route, selected from the group consisting of soft or hard gelatin capsules, tablets, solutions, suspensions and emulsions.
Such a pharmaceutical composition is preferably intended for oral administration, in a gastroresistant form.
The subject of the present invention is also other applications of the said C-terminal peptide of pancreatic lipase, for example as diagnostic reagent, in particular in the carrying out of an immunoenzymatic test for the assay of lipase by a competitive-type method and in the carrying out of methods of controlled lipolysis of triglyceride substrates.